The invention refers to a magnet assembly for the contact-less detection of the position of an axially displaceable bar having a collar or a circumferential groove, preferably a shift rod of an automatic transmission, which magnet barrier has a magnetic field sensor directed at the rod.
Magnet barriers of this type are generally known and customary.
In the known magnet assemblies a magnet is generally attached to the rod to be monitored, so that a signal is produced when the rod is opposite a magnetic field sensor which is arranged alongside the rod. Such an arrangement has the disadvantage that the application of the magnet to the rod is expensive and the rod must be installed in a fixed alignment with respect to the magnetic field sensor and remain therein. These disadvantages can be avoided if the magnet is arranged directly on the magnetic field sensor and the shaft is provided, for instance, with a collar on which the lines of flux are concentrated when the collar is below the magnet and magnetic field sensor. Such an arrangement has the disadvantage, however, that there is a high residual field strength for the magnetic field sensor when the collar is outside the range of the magnetic field sensor. As a result, the magnet assembly operates unreliably, particularly in the assembly of large air gaps.